Localip: uses assigned netlink port id on Linux (#2253)

Fixes #2252

Author: txhno

src/common/impl/netif_linux.c

@@ -7,6 +7,18 @@
 #include <linux/rtnetlink.h>
 #include <net/if.h>
 
+static uint32_t ffNetifGetNetlinkPortId(int sock_fd) {
+    struct sockaddr_nl addr = {};
+    socklen_t addrLen = sizeof(addr);
+    if (getsockname(sock_fd, (struct sockaddr*) &addr, &addrLen) < 0) {
+        FF_DEBUG("Failed to query netlink socket address (use PID instead): %s", strerror(errno));
+        return instance.state.platform.pid;
+    } else {
+        FF_DEBUG("Netlink port ID: %u", addr.nl_pid);
+        return addr.nl_pid;
+    }
+}
+
 bool ffNetifGetDefaultRouteImplV4(FFNetifDefaultRouteResult* result) {
     FF_DEBUG("Starting IPv4 default route detection");
 
@@ -17,9 +29,6 @@ bool ffNetifGetDefaultRouteImplV4(FFNetifDefaultRouteResult* result) {
     }
     FF_DEBUG("Created netlink socket: fd=%d", sock_fd);
 
-    uint32_t pid = instance.state.platform.pid;
-    FF_DEBUG("Process PID: %u", pid);
-
     // Bind socket
     struct sockaddr_nl addr = {
         .nl_family = AF_NETLINK,
@@ -33,6 +42,8 @@ bool ffNetifGetDefaultRouteImplV4(FFNetifDefaultRouteResult* result) {
     }
     FF_DEBUG("Successfully bound socket");
 
+    uint32_t pid = ffNetifGetNetlinkPortId(sock_fd);
+
     struct __attribute__((__packed__)) {
         struct nlmsghdr nlh;
         struct rtmsg rtm;
@@ -228,9 +239,6 @@ bool ffNetifGetDefaultRouteImplV6(FFNetifDefaultRouteResult* result) {
     }
     FF_DEBUG("Created netlink socket: fd=%d", sock_fd);
 
-    uint32_t pid = instance.state.platform.pid;
-    FF_DEBUG("Process PID: %u", pid);
-
     // Bind socket
     struct sockaddr_nl addr = {
         .nl_family = AF_NETLINK,
@@ -244,6 +252,8 @@ bool ffNetifGetDefaultRouteImplV6(FFNetifDefaultRouteResult* result) {
     }
     FF_DEBUG("Successfully bound socket");
 
+    uint32_t pid = ffNetifGetNetlinkPortId(sock_fd);
+
     struct __attribute__((__packed__)) {
         struct nlmsghdr nlh;
         struct rtmsg rtm;